This application relates to optical fiber communication devices, and more particularly, to techniques and devices for signal processing in wavelength-division multiplexed fiber systems.
A wavelength-division multiplexed (WDM) fiber system can be used to transmit different channels of signals carried by optical carriers at different WDM wavelengths in a single fiber. Hence, the transmission capacity of a fiber link can be increased.
The power levels of different WDM channels, however, may be different from one another due to factors such as differences in the signal sources and transmission paths. This variation in signal strength of different WDM channels at a location in a fiber link may cause difficulties in a number of areas in the fiber system, including but not limited to, conditioning the signals during the transmission and relay, signal detection and data extraction. It is therefore desirable to implement devices in a fiber system to independently adjust the power levels of different WDM channels and thus to substantially equalize the signal strengths.
This application includes devices that couple variable attenuators to a single WDM multiplexer to independently adjust and control power levels of individual WDM channels and to substantially equalize the power levels of different WDM channels if so desired. The structures of such devices are simple, compact, and may be manufactured at low cost.
One embodiment of the devices includes an input optical terminal, an optical multiplexer coupled to the input optical terminal, a plurality of variable attenuators, and a reflector. The input optical terminal is used to transmit a WDM signal having a plurality of optical signals at different WDM wavelengths. The optical multiplexer is adapted to have a plurality of output optical terminals and is operable to separate the optical signals at different WDM wavelengths into the output optical terminals, respectively.
The variable attenuators are respectively coupled in the output optical terminals to independently attenuate the optical signals in response to respective control signals so as to produce first attenuated signals. The optical reflector is coupled to the output optical terminals to receive and reflect the first attenuated signals back to the variable attenuators which generate second attenuated signals respectively traveling in the output terminals towards the optical multiplexer. The optical multiplexer is operable to combine the second attenuated signals to produce an attenuated WDM signal in the input optical terminal.